The dynamics of viral shedding and symptoms following influenza virus infection are key factors when considering
epidemic control measures. The authors reviewed published studies describing the course of influenza virus
infection in placebo-treated and untreated volunteers challenged with wild-type influenza virus. A total of 56
different studies with 1,280 healthy participants were considered. Viral shedding increased sharply between 0.5
and 1 day after challenge and consistently peaked on day 2. The duration of viral shedding averaged over 375
participants was 4.80 days (95% confidence interval: 4.31, 5.29). The frequency of symptomatic infection was
66.9% (95% confidence interval: 58.3, 74.5). Fever was observed in 37.0% of A/H1N1, 40.6% of A/H3N2 (p ¼ 0.86), and 7.5% of B infections (p ¼ 0.001). The total symptoms scores increased on day 1 and peaked on day 3.
Systemic symptoms peaked on day 2. No such data exist for children or elderly subjects, but epidemiologic studies
suggest that the natural history might differ. The present analysis confirms prior expert opinion on the duration of
viral shedding or the frequency of asymptomatic influenza infection, extends prior knowledge on the dynamics of
viral shedding and symptoms, and provides original results on the frequency of respiratory symptoms or fever.
influenza, human; signs and symptoms; virus shedding